This article investigates the writings of Danish science journalist Børge Michelsen from 1939 to 1956. As part of the international social relations of science movement in the period, Michelsen transformed science journalism from mere reporting on issues pertaining to science into performing the social function of science journalism: advancing and enacting the social relations of science. Based on analyses of Michelsen's articles and other initiatives, this study suggests that the social function of science journalism practiced by Michelsen showed many new and conflicting aspects. From a boundary-work perspective, it is argued that, through science journalism, Michelsen not only helped establish new cultural boundaries of science, but also did anti-boundary-work. The notion of anti-boundary-work implies breaking down existing barriers between science and society, all the while establishing new links to reinforce mutual relations between scientists and policy-makers, between scientists and journalists, and between science and the public. Finally, in the concluding remarks, the contemporary significance of Michelsen's social function of science journalism is discussed.